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<TITLE>Example Program: Roots of a Polynomial</TITLE>
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<H2>20.3 Example Program: Roots of a Polynomial</H2>
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<BLOCKQUOTE><HR><B>
NOTE -- This program is in the file complx.cpp.
</B><HR></BLOCKQUOTE>
<P>The roots of a polynomial <IMG SRC="images/stdlibug-SpecialClassesa.gif" WIDTH=128 HEIGHT=29>are given by the formula:</P>
<P><IMG SRC="images/stdlibug-SpecialClasses2.gif" WIDTH=177 HEIGHT=71></P>
<P>The following function takes as input three double precision numbers, and returns the complex roots as a pair of values.</P>

<UL><PRE>
typedef std::complex&lt;double&gt; dcomplex;

std::pair&lt;dcomplex, dcomplex&gt; quadratic
      (dcomplex a, dcomplex b, dcomplex c)
// return the roots of a quadratic equation
{
   dcomplex root = std::sqrt(b * b - 4.0 * a * c);
   a *= 2.0;
   return std::make_pair( (-b + root)/a, 
                          (-b - root)/a );
}
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